Emissions from conventional internal combustion gasoline engines are formed when hydrocarbon fuel, as gasoline, is burned incompletely into hydrocarbon (HC) and carbon oxides (CO). The formation of pollutant CO, HC and nitrous oxide (NO.sub.x) is a function of the proportional amounts of air and fuel introduced into the combustion chamber. The effect of the air-to-fuel ratio on the exhaust composition of these pollutants is shown in the graph of FIG. 1. Lean air-to-fuel ratios have decreased CO and HC emissions because of the greater quantity of oxygen available for combustion. When the air-to-fuel ratio becomes too lean (below 14:1), both HC and CO emissions increase.
NO.sub.x emissions are an exponential function of flame temperature. At low temperatures, nitrogen and oxygen will not unite to form any significant amount of NO.sub.x. Low temperatures are achieved at both rich and lean air-to-fuel ratios because of the dilutant effect exerted by unburned fuel in the rich case and the excess of air in the lean case.
When the internal combustion engine operates at its stoichiometric point, the amount of fuel is matched exactly with the amount of oxygen for complete combustion. This point falls somewhere between 14.5 and 15 pounds of air per pound of fuel. The operation of an engine at this point produces the maximum amount of NO.sub.x. An air-to-fuel mixture of 18-20 pounds of air per pound of fuel will produce the least CO, HC and NO.sub.x emissions.
Internal combustion engines will operate effectively at air-to-fuel ratios of 18:1 or even leaner ratios. The operation of the engine under these conditions is contingent on getting the right air-to-fuel mixture into all of the cylinders. With present carburetor technology, the air-to-fuel ratio of the fuel mixture to all of the cylinders is not constant. Some of the cylinders will be fed properly while others will be too lean. Others may be too rich. In either circumstance, there will be an increase in emissions.
Hydrocarbon fuels have a small percentage of foreign liquids and particulate matter, as water, oils, non-combustible carbon, and dirt. These foreign products cause dirt build-up in the carburetor and inefficient fuel-to-air ratios.
Hydrocarbon fuel vapor and air mixing devices have been developed. These devices have structures for heating or elevating the temperature of the fuel prior to the release to the intake manifold of the engine. Examples of fuel vaporizing and air mixing devices are shown in U.S. Pat. Nos. 3,509,859; 3,847,128 and 3,872,848.
High frequency ultrasonic generators having piezoelectric ceramic crystals have been used for ultrasonic cleaning operations and in the material testing field. Other applications include medical and chemical uses for emulsifying and dissolving purposes. Examples of high frequency ultrasonic generators are shown by Scarpa in U.S. Pat. No. 3,433,161 and Rodudo et al in U.S. Pat. No. 3,904,347.
A monodisperse aerosol generator is disclosed by Berglund and Liu in U.S. Pat. No. 3,790,079. This generator has an ultrasonic vibrator that acts on a disc having a discharge orifice. The liquid moving through the orifice is subjected to ultrasonic vibrations which break the liquid down to substantially equal size droplets which are discharged into a chamber.